Embodiments of this invention generally relate to integrated circuits for signal processing. More particularly, embodiments of the invention relate to the field of Digital-to-Analog Converter (DAC) for Audio signals and provide methods and systems for oversampling DACs.
In current-steering DACs, switches are used to route current into sensing elements that can measure the amount of current flowing. The switches are driven by the digital value representing the number to be converted to analog, and the amount of current sensed becomes the analog value. As the number of bits and precision requirement increase, the number of components can also increase exponentially. In noise-shaping D/A converters, it is often necessary to remove large amounts of out-of-band noise produced by the digital modulator. An approach is to use a multi-bit noise-shaper, where the quantizer truncates the digital word to more than 1 bit. However, errors in the digital-to-analog converter used to turn the multi-bit digital signal into an analog voltage will cause linearity errors in the analog output. Proposals have been made of ways to use “scrambling” techniques to minimize the linearity problem with multi-bit noise-shapers. The “scrambling” arrangements often require that the multi-bit output of the noise shaper first be converted to a “thermometer code” in which all of the bits are equally weighted. In some thermometer encoders, an N-bit digital data is represented by K=2N bits of 0's and 1's. For example, a 5-bit binary code converted to a thermometer code would require 31 equally-weighted bits (the “all bits off” state does not require an output bit). If the input number was “11”, then the thermometer code would have the bottom 11 bits set to a “1” and the top 20 bits set to “0”.